One known type of information storage device is a disk drive device that uses magnetic media to store data and a movable read/write head that is positioned over the media to selectively read from or write to the disk.
FIG. 1a illustrates a conventional disk drive device and shows a magnetic disk 101 mounted on a spindle motor 102 for spinning the disk 101. A voice coil motor arm 104 carries a head gimbal assembly (HGA) 100 that includes a slider 103 incorporating a read/write head. A voice-coil motor (VCM, not labeled) is provided for controlling the motion of the motor arm 104 and, in turn, controlling the slider 103 to move from track to track across the surface of the disk 101, thereby enabling the read/write head to read data from or write data to the disk 101. In operation, a lift force is generated by the aerodynamic interaction between the slider 103 and the spinning magnetic disk 101. The lift force is opposed by equal and opposite spring forces applied by the HGA 100 such that a predetermined flying height above the surface of the spinning disk 101 is maintained over a full radial stroke of the motor arm 104.
Now referring to FIGS. 1b-1c, a conventional HGA 100 comprises the slider 103, a suspension 190 to load or suspend the slider 103 thereon. As illustrated, the suspension 190 includes a load beam 106, a base plate 108, a hinge 107 and a flexure 105, all of which are assembled together.
The load beam 106 is connected to the base plate 108 by the hinge 107. A locating hole 112 is formed on the load beam 106 for aligning the load beam 106 with the flexure 105. As best shown in FIG. 1e, a dimple 111 is formed on the load beam 106 to transfer load forces generated by the load beam 106 to the flexure 105 at a position corresponding to a center of the slider 103. By this engagement of the dimple 111 with the flexure 105, the load forces can be transferred to the slider 103 uniformly, thus making the slider 103 working more stably.
The base plate 108 is used to enhance structure stiffness of the whole HGA 100. A mounting hole 113 is formed on end of the base plate 108 for mounting the whole HGA to the motor arm 104 (refer to FIG. 1a). The hinge 107 has a mounting hole 110 formed on its one end corresponding to the mounting hole 113 of the base plate 108, and the hinge 107 is partially mounted to the base plate 108 with the mounting holes 110, 113 aligned with each other. The hinge 107 and the base plate 108 may be mounted together by laser welding at pinpoints 109 distributed on the hinge 107. Two hinge steps 115 are integrally formed at two sides of the hinge 107 at one end adjacent the mounting hole 110 for strengthening stiffness of the hinge 107. In addition, two hinge struts 114 are extended from the other end of the hinge 107 to partially mount the hinge 107 to the load beam 106.
The flexure 105 runs from the hinge 107 to the load beam 106. The flexure 105 has a proximal end 119 adjacent the hinge 107 and a distal end 118 adjacent the load beam 106. A locating hole 117 is formed on the distal end 118 of the flexure 105 and aligned with the locating hole 112 of the load beam 106, thus obtaining a high assembly precision.
FIG. 1d shows the tip part of the flexure 105 and illustrates the top-face side of the flexure 105 on which the slider 103 is mounted. As shown in FIG. 1d, the flexure 105 of the suspension 190 has a suspension tongue 116 with which almost an entire surface of one face of the slider comes in contact and fixed. The suspension tongue 116 is also referred to as a gimbal whose one end is connected to the flexure 105, and the connection part exhibits a spring characteristic which functions to allow the loaded slider 103 to keep a proper flying height with respect to the disk 101.
The suspension tongue 116 and the slider 103 are securely fixed by an adhesive filled therebetween. Further, there are cases of using solder for fixing the slider 103, whether or not the adhesive is used.
FIG. 1e illustrates the slider 103 flying above the magnetic disk 101 when the HDD is working. In a common disk drive unit, the slider flies only approximately a few micro-inches above the surface of the rotating disk. Generally, the flying height “h” of the slider, shown in FIG. 1e, is considered as one of the most critical parameters affecting the disk reading and writing performances. More concretely, a relatively small flying height allows the transducers impeded on the slider to achieve a greater reading/writing resolution between different data bit locations on the disk surface, thus improving data storage capacity of the disk. Therefore, it is desired that the slider have a very small flying height to achieve a higher data storage capacity. At the same time, with the increasing popularity of lightweight and compact notebook type computers that utilize relatively small yet powerful disk drives, the need for a progressively lower and lower flying height has continually grown.
With reduction of the flying height, it is strongly expected that the flying height be kept constant all the time regardless of variable flying conditions, since great variation of flying height will deteriorate reading/writing performance of the slider, and in worse cases even result in data reading/writing failure.
If coefficients of thermal expansion (CTE) of the slider 103 and the flexure 105 are different, the slider 103 may have a warp and distortion in accordance with deformation of the suspension tongue 116 caused by heat. FIG. 2a schematically shows an example thereof. As shown in FIG. 2a, when both ends of the slider 103 are connected to the suspension tongue 116 by the solders 130, the suspension tongue 116 shrinks and changes its shape as shown by arrows of FIG. 2b at a low temperature. In accordance with this, there is a warp (crown) generated in the slider 103. The suspension tongue 116 is extended in arrows of FIG. 2c when the temperature increases, which also causes the slider 103 to have a crown.
The deformation of the slider 103 described above can also happen in the case where the suspension tongue 116 and the slider are securely fixed by adhesive.
FIG. 2f shows a stress distribution of the thermal expansion caused in the flexure 105 when the flexure 105 in the shape of FIG. 1d is heated to 55° C. In this illustration, the part with lighter shading is where more stress is concentrated. From the illustration, it can be seen that the stress concentrates on the soldered part. Thus, the stress is also imposed on the slider 103 that is fixed by solder at that soldered part. In other words, the stress may cause deformation of the magnetic head slider 103 as described above. In a worse case, the solder 130 may be generated a crack 131 under the stress, as shown in FIG. 2d-2e. 
The deformation of the slider will cause the variation of the flying height thereof, thereby badly affecting reading/writing performance of the slider. Further, the deformation may cause crack of the solder, thereby cutting the electrical connection of the slider 103 and the flexure 105. Therefore, it is necessary to control the deformation to a tolerant limit.
Referring to FIG. 3, the air bearing surface (ABS) of the slider has morphological characteristics such as a total crown and a cross crown. The total crown is the maximum height of a convex surface provided in the longitudinal direction that is an inflow direction of air to or an outflow direction of air from the slider. The cross crown is the maximum height of a convex surface provided in the cross direction, which is orthogonal to the longitudinal direction. The changes of flying height are affected by the slider total crown and the cross crown simultaneously. Normally, the total crown is more sensitive than cross crown and its criterion is usually less than 1 nm in specification.
Hence, a need has arisen for providing an improved suspension which can release thermal deformation of the suspension tongue and suppress thermal crown change of a slider mounted thereon.